How do you know for sure if what you have to say is meaningful? Haven't you ever found yourself mistaken about that, saying something you feel is meaningful but then getting convincingly corrected on it? To solve that, I think it's okay and good to let subjective meaning qualify as "meaningful" when you're considering whether to say something, but not assume that said subjective meaning will always survive objective processing. If it doesn't, it was still worth speaking up because it shows you are willing to contribute.

What do you think about thinking something you're quite sure is valuable to the situation, but not saying it - whether out of fear, apathy, or otherwise? That omission is what I think of when I think of silence. I find this morally dicier than blurting something that is meaningless. In fact, being expected to have a justifying purpose ready literally every time one opens their mouth feels a little draconian in that it would silence a lot of fun and play along with the noise you aim to eliminate, although its a good guideline to follow in more or less moderation depending on the situation.

tl;dr - know the right time for silence and the right time to say your piece, and have the courage and discipline to follow through with that knowledge. And other times, it's excessive to worry about these things, so relax then.

Being silent just makes you lonely, because everyone in the whole world hates people who are silent. According to literally everyone but me, if you are silent you deserve to be ostracized. This is the worst idea I've ever heard of, no offense to you.